.
See the website: The Fabulous RISC Relay Computer which offers documentation, an emulator, and some software to run on it.

There's a video too: "This is the first video of the RISC Relay CPU. The cpu is not yet complete. When finished, it will be a lot faster and it will function as a scientific calculator."

i like the conception of relay processors, but i personally would vote on TTLs

We've a few previous threads on TTL machines... (that's just a text search, won't be 100% accurate, so see also here and here)